During the past years we have studied foreign body (FB) tumorigenesis in mice. We have established the nature and the monoclonal origin of tumor originator cells, have revealed FB-tumorigenesis as a multistage developmental process, and have learned about the changing etiologic role of the FB during the various sequential stages of the tumorigenic process. We recently found a method to culture, clone and expand in vitro the tumor originator cells during specific stages of preneoplastic development. We now propose to derive in vitro clonal populations of tumor originator cells from the in vivo preneoplastic tissue at different defined stages of preneoplastic development beginning with the normal state up to full neoplastic autonomy. The availability of such cell preparations would permit comprehensive sequential analyses of cellular changes associated with the carcinogenic process. Specifically the following areas of study are called for: Histopathology, ultrastructure, chromosome cell growth kinetics (especially determination of proliferative thresholds), conditions for and degrees of in vivo tumorigenicity, cellular interactions, membrane phenomena, further (in cooperation with other laboratories) cellular biochemistry and regulation, cell genetics, membrane structure and function, and possibly other specialized areas of cell research.